In recent years, hybrid vehicles and electric vehicles, which include a rotating electrical machine as a driving force source, have attracted attention in order to achieve energy saving and reduction in environmental burdens. Such vehicles are provided with a DC power supply such as a battery which supplies electric power when the rotating electrical machine functions as a driving force source, and which stores electric power generated when the rotating electrical machine functions as an electric generator. Since an AC rotating electrical machine is often used as the rotating electrical machine, an inverter device including an inverter circuit that converts electric power between DC power and AC power is mounted on such vehicles. Such an inverter device is also used in power control devices etc. However, especially when such an inverter device is mounted on vehicles, reduction in size of the inverter device is desired due to limitations on weight and mounting space, etc. Moreover, since the inverter circuit uses a component generating a large amount of heat such as a power module having a power switching element, a cooling mechanism is required to cool the inverter device. Accordingly, attempts have been made to implement an integrated device by accommodating the inverter circuit in, e.g., a case provided with cooling fins etc. and to reduce the size and weight of the inverter device.
For example, Japanese Patent Application Publication No. 2009-106046 (JP 2009-106046 A) (Patent Document 1) discloses an example of such an integrated inverter device. In this inverter device, a power module is placed on a flat surface in a case having a heat dissipating portion. A smoothing capacitor electrically connected to the power module is placed on a flat surface that is slightly lower than the flat surface on which the power module is placed, such that the smoothing capacitor adjoins the power module (seventh and eighth paragraphs, FIG. 1, etc.). A smoothing capacitor that is desired to have a high breakdown voltage and large capacitance tends to have a large physical size. In Patent Document 1, since the heat dissipating portion and the power module are placed so as to correspond to the height of the smoothing capacitor, the overall height of the inverter device can be reduced. However, in the case of this case, both the power module and the smoothing capacitor need be fixed to the case by bolts etc. For example, in FIG. 1 of Patent Document 1, the power module is fixed to the case by bolts, but the smoothing capacitor is merely fastened to electrodes extending in the horizontal direction from the power module by bolts. Providing a separate structure for fixing the smoothing capacitor to the case requires a space for the fixing structure for both the smoothing capacitor and the case, which may hinder reduction in size of the inverter device.